1. Field of the Invention
The present invention relates to a resistor-capacitance (RC) calibration circuit, and more particularly, to an RC calibration circuit using a single current source.
2. Description of the Prior Art
In integrated-circuitry (IC), poles and zeros of frequency response, current sources and biasing voltages are usually implemented by passive components such as resistors and capacitors. Real values of the passive components, however, will deviate from the designed value due to variations of process, voltage and temperature (PVT). As a result, the poles and zeros of the frequency response are hard to control, meaning currents of current sources and the voltages of biasing points will also deviate from the designed values. Performance of the integrated circuitry is significantly reduced.
For example, when a filter of an integrated circuit is implemented in a resistor and a capacitor, a pole and a zero of the filter are directly related to a resistance R of the resistor and a capacitance C of the capacitor C. The frequency response of the filter is decided by the resistance R and the capacitance C. If the resistance R and the capacitance C—vary with process variation, the frequency band of the filter will deviate from the desired frequency band of the circuit system, such that the overall performance of the integrated circuit is decreased.
To overcome the above problems, a conventional method uses a resistance-capacitance (RC) calibration circuit to correct the deviation of the resistance R and the capacitance C and thereby improve the overall performance of the integrated circuit. The RC calibration circuit uses multiple current sources to generate a plurality of voltages utilized for RC calibration processes. The current of each current source will vary, however, due to process variations, the result being that the plurality of voltages will deviate from their designed values. As a result, current mismatches generated from the process variation decrease the accuracy of the RC calibration circuit and worsen the overall performance of the integrated circuit.